@Informaton: Oh, it's nothing; just a cheating script ("gaming the test suite answers") combined with the well-known 'regexp' trick. A proper small solution was first submitted by Tim (Solution 97452 - size:51) and was later optimized in size by Alfonso Nieto-Castanon (Solution 181060 - size:48). My alternative Solution 1198643 (size:63), which uses for-loops instead of conv2 or filter2 function, is also much better than this 'regexp' cheat.